Conformational analysis of the methyl ester of alanine by gas electron diffraction and Ab initio geometry optimization |
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Authors: | John D. Ewbank, V. Joseph Klimkowski, Khamis Siam,Lothar Sch fer |
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Affiliation: | Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701 U.S.A. |
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Abstract: | The gas electron diffraction data of the methyl ester of l-alanine were recorded at an approximate nozzle temperature of 80°C and analyzed with geometrical constraints taken from 4-21G ab initio gradient geometry refinements. The molecular intensities are consistent with a model for the most populated conformational state in which the NCCO torsion (τ) is syn-peri-planar and a bifurcated hydrogen bond exists between NH2 and CO. Details of the intensity data make it impossible to rule out the presence of significant concentrations of a second conformer, (τ ⋍ + 150°), in contrast to the ab initio calculations which predict greater stability of the system at τ ⋍ −150° than +150°. |
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